Zeus, a virus that steals online banking details from infected computer users, is more powerful than ever, warns a web security company.

Trusteer says it has spotted the Trojan virus in one of every 3,000 of the 5.5m computers it monitors in the US and UK.

Zeus 1.6 can infect people using Firefox and Internet Explorer web browsers, the company claims.

The malware steals login information by recording keystrokes when the infected user is on a list of target websites.

These websites are usually banks and other financial institutions.

The user’s data is then sent to a remote server to be used and sold on by cyber-criminals.

“We expect this new version of Zeus to significantly increase fraud losses, since nearly 30% of internet users bank online with Firefox and the infection is growing faster than we have ever seen before,” said Amit Klein, chief technology officer at Trusteer.